That would be a solution, however so far I haven't found such a 'thiskeyisdown' kind of method that I can use, apart from AltDown, ShiftDown, CmdDown, MetaDown and ControlDown. What I'm looking for is a way to check if any other key besides those is currently down.

I'm too busy at the moment to go and check. But isn't there a function that returns a boolean (true/false) value of whether a key is pressed down or not? Did you try checking the wxPython samples for such an example? I'm pretty sure I remember seeing this there.